1. Field of the Invention
This invention relates to a heating apparatus for a vehicle interior which uses coolant for an engine powering a vehicle body.
2. Description of the Related Art
A conventional heating apparatus for a vehicle interior uses coolant for an engine powering a vehicle body. Specifically, the conventional heating apparatus includes a heater core disposed within a duct. The engine coolant is supplied to the heater core as heating fluid. Air flowing in the duct is heated by the heater core before being discharged into the vehicle interior.
In some efficient engines of the diesel type or the lean-burn type, engine coolant tends to be only heated to an insufficient temperature at which the engine coolant inadequately heats a heater core.
U.S. Pat. No. 4,993,377 corresponding to Japanese published unexamined patent application 2-246823 discloses an automobile heating apparatus. The automobile heating apparatus of U.S. Pat. No. 4,993,377 includes a water pump for circulating the cooling water for an automobile powering engine, a radiator for heating the air to be introduced into the automobile room by utilizing the cooling water delivered by the water pump as a heat source, and a hot water circuit for circulating the cooling water in the automobile powering engine, the water pump, and the radiator. A heat generator is disposed in the hot water circuit at an upstream portion with respect to the radiator. The heat generator includes a heat generating chamber having a labyrinth groove and containing viscous fluid therein, a housing disposed adjacent to the heat generating chamber and having a heat receiving path constituting part of the hot water circuit, a shaft rotatably held in the housing and receiving the rotary torque of the automobile powering engine by way of clutch means, and a rotor fixed on the shaft at an end thereof and having a labyrinth groove disposed in the heat generating chamber.
In the automobile heating apparatus of U.S. Pat. No. 4,993,377, the heat generator includes a shearing-based heater. Specifically, when the clutch means couples the shaft with the output shaft of the automobile powering engine, the shaft is rotated by the engine output shaft and thus the rotor is also rotated. The rotor applies a shear force to the viscous fluid in the heat generating chamber while rotating. The applied shear force causes the viscous fluid to be heated. The cooling water is heated as the viscous fluid is heated. As a result, the cooling water can be heated to a sufficient temperature or a desired temperature.
A related drawing in U.S. Pat. No. 4,993,377 shows that the clearance between the rotor and the housing is very small. Accordingly, it appears that the rotor tends to be locked to the housing by a cause such as deformation of the rotor relative to the housing or movement of a foreign body into the clearance.
Japanese published unexamined patent application 6-92134 discloses a heating apparatus for a vehicle which includes an auxiliary heater of a shearing-based type. In the heating apparatus of Japanese application 6-92134, a portion of coolant flows from the body of a vehicle powering engine to an air-heating core via the auxiliary heater. The auxiliary heater contains viscous fluid. The auxiliary heater has a shaft. As the shaft is rotated, a shear force is applied to the viscous fluid. The applied shear force causes the viscous fluid to be heated. The coolant in the auxiliary heater is heated as the viscous fluid is heated. The shaft of the auxiliary heater is connected to the output shaft of the vehicle powering engine via an electromagnetic clutch and a power transmission mechanism using a belt. When the electromagnetic clutch is in its engaged position, the shaft of the heater can be rotated by the output shaft of the vehicle powering engine. When the electromagnetic clutch is in its disengaged position, the shaft of the heater is uncoupled from the output shaft of the vehicle powering engine.
In the heating apparatus of Japanese application 6-92134, a temperature sensor detects the temperature of coolant directed from the body of the vehicle powering engine to the auxiliary heater. When the detected temperature of the coolant is relatively low, a computer-based controller sets the electromagnetic clutch in its disengaged position to suspend operation of the auxiliary heater.